It is common in the radio arts to electromagnetically shield or protect certain circuitry by enclosing the protected circuitry in a conductive structure or housing that is coupled to a ground potential. The goal of conventional electromagnetic shielding practice is to prevent or sufficiently reduce radiated electromagnetic interference (EMI) such that the device performs properly or conforms to specifications such as those required by the Federal Communications Commission (FCC). EMI is caused by unrestricted electrical and magnetic energy that escapes from any electrical device and reaches a second unintended device. It is called EMI if the receiving device malfunctions as a result of this "pollution". For most practical purposes, the majority of EMI problems are limited to a part of the electromagnetic spectrum from 1 kHZ to 10 GHZ. This portion of the electromagnetic spectrum is known as the radio frequency interference (RFI) band and covers the radio and audio frequencies.
Techniques which offer protection against RFI are varied, but generally seek to block the sensitive circuitry from the RFI signal. Placing a Faraday Cage around an electrical device is the fundamental principle underlying the housing techniques for shielding against RFI. Most often the housing approach to shielding is applied to the external housing of the entire device. However, the approach can be applied as an internal shielding mechanism. In this case, a mini box that is electrically conductive is used to isolate the susceptible components. The result is the creation of a mini Faraday Cage inside the finished device.
Problems occur, however, when information or signals must be transferred between the protected circuitry and other circuitry within the device. To do this, apertures are typically required to be formed in the shielding structure to permit a connector or the like to pass through the aperture to conduct signals or information into and/or out of the shielding structure. Depending on the size of the connectors, and hence the apertures, the effectiveness of the shielding structure may be compromised. Moreover, even if the radiated interference is not increased by the presence of the aperture in the shielding structure, interference within the shielding structure may be radiated into the wires or conductors coupled to the connector, and thus conduct interference outside the shielding structure to contaminate other circuitry. Accordingly, there is a need in the art for a technique to electromagnetically shield electronic circuitry while permitting information to be readily passed between the shielded circuitry and other circuitry.